Amidon/Palomar For RFI For Coils For Balun transformer
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#67 mu = 40 10-80 MHz 10-800 MHz
#61 mu = 125 100-2GHz .2-10 MHz 100 kHz - 30 MHz
#43 mu = 850 1-1000 MHz .01-1 MHz 10 kHz -100 MHz
#77 mu = 1800 .5-100 MHz 1-100 kHz 1 kHz - 2 MHz
F-240 means ID = 1.4 inch, OD=2.4 inch